1. Field of the Invention
The invention relates to a method for producing index prints having a selectable number of small positive images of associated photographic originals.
2. State of the Art
When customers turn in exposed film material for processing, the exposed film material is typically developed in the photo laboratory in order to obtain photographic originals, from which photographic copies or prints are then made by a photographic printer. Very often in the industry, the film material is negative films which are developed in the photo laboratory. In that case, the photographic originals are the individual frames on the developed negative film strips, and the photographic copies produced from them are paper prints. Hereinafter, for the sake of simplicity, this situation will be referred to by way of example; that is, the frames located on the negative films will be taken as a representative example of photographic originals, and the paper prints as a representative example of photographic copies. Naturally slides, for example, can also serve as originals from which copies are made, and photographic copies can be in the form of sheets.
Once a customer order has been processed, the customer typically receives the developed negative films in the form of strips of film that each contain from 4 to 6 frames, for instance, together with the paper prints. The customer often then keeps the negative film strips in a separate place from the paper prints. For instance, the paper prints are arranged in a photo album, and the negative film strips are collected at a separate location. If the client later wants to order reprints, it is often quite difficult, especially for an amateur photographer, to identify the desired image on the negative film strips. Especially with color negative film, it is very difficult for an unskilled person to assess the picture content of frames on the negative film strips, because of the color reversal and the film mask. So-called index prints make this task much easier. An index print is a single paper copy, for instance of the same size as a paper print, but that contains a plurality of small single images that belong to different frames on the negative film and are shown in the form of small positive images.
By way of example, all the frames on a negative film can be shown on such an index print, in the form of a matrix of individual small positive images. Besides the individual pictures, the index print typically also contains other information. For instance, for each individual picture it can be noted what the number of the associated frame on the negative film is. Other individual frame information, generated individually during the production of the index print or located on the negative film and read off from it, can also be included. The index print can also contain order-specific data, such as the film identification number, as well as a company logo, such variable information as the date, and so forth.
For the customer, the index print meets a practical need, because he can find out what a negative film contains from the small positive images without having to look at the film itself or touch it. The difficulties in assessing the negative film because of the color reversal are thus circumvented. Index prints are also highly advantageous for ordering reprints. On one hand, the customer can easily identify the desired frame, without making mistakes, from the small positive images with the associated negative numbers. On the other, he no longer has to hold the negative strips in his hand, thus markedly reducing the danger of damage to the negative film strip, from scratches, dirt, dust or fingerprints, that are deleterious to the quality of paper reprints.
The index print is thus a kind of "table of contents" of a photo album and is especially advantageous and customer- friendly for ordering reprints. For the future, and also in view of recent developments in the field of photographic materials and the increasing significance of video technology (such as photo CDs), it can therefore be expected that index prints will gain markedly greater significance and will become standard in photoprocessing. Hence there is a strong need for photographic printers, with which photographic copies of photographic originals are produced, also to be capable either of producing such index prints directly or of furnishing the necessary data in digital form for an external device.
Currently known technologies for producing index prints can be roughly divided into two categories. The first category includes methods in which the index prints are produced in purely optical photographic ways. The frames on the negative film are copied by optical projection, on either a natural or a reduced scale, onto photographic paper, or photo paper for short. The individual images in the matrix of the index print are projected in sequence, directly from the originals on the negative film, purely photographically onto photo paper using a special lens. In principle--aside from the different scale of enlargement and the matrixlike arrangement of individual pictures--there are hardly any differences from the classical mode of operation of a photographic printer. This purely photographic technology has been described for instance in European Patent Disclosure EP-A 0 697 628. Although the method proposed in this reference is in principle absolutely functional and powerful, it does have limitations. For instance, the index print must be produced using a photographic printer and cannot be produced by some other output device.
In the second category, the technology is markedly different. Here, the original (frame) is first broken down by an optical scanner into a large number of individual pixels, which in turn are split up into three colors, represented as digital numerical values, and stored in memory. From the thus-stored picture contents of a number of successive frames of a negative film strip, small images combined into an index print are then produced using a color printer or picture output device of suitable design (CRT printer, thermal printer, laser printer, or the like). Examples of this technology are found in U.S. Pat. Nos. 4,903,068, 4,933,773, 5,184,227 and 5,400,152.
In U.S. Pat. No. 4,903,068 for producing a photographic copy (image frame), the original is exposed regionally in the exposure station of the photographic printer with an unmodulated light spot of a black-white cathode ray tube (CRT) and transmitted onto photo paper in color sequence via a projection lens and three color filters. During this process, some of the light of the light spot, once it has passed through the original and before it reaches the projecting lens, is deflected to a photoreceiver by a partly reflective mirror. The image signals thus produced are digitized and stored in memory for each frame of the negative film in the form of a data set, with three color density values per pixel. After a selectable, predetermined number of copied frames at a time, the stored image signals are called up from the memory and electronically processed into a composite picture with a corresponding number of reduced-size pictures. This composite picture is shown, as a negative black and white image for each component color, on the same cathode ray tube by which the photographic copies were produced, and its image light can thus be projected as an index print onto the photo paper.
A similar method is disclosed in U.S. Pat. No. 4,933,773. Here, however, a conventional halogen incandescent lamp serves as a light source for projecting the original onto photo paper. The difference and the advantage over U.S. Pat. No. 4,903,068 is that all the pixels are transmitted simultaneously, thus shortening the exposure time required. To produce the index print when the image light of an original is projected, some of the copying light, after passing through the original, is reflected out to a video camera. The video camera receives the picture information, divides it up by color, encodes it digitally, and stores it in memory. Once the predetermined number of frames have been projected, the associated digitally stored picture information is called up in diluted form and grouped into a matrix, and a negative index print is produced. This is shown on a cathode ray tube and is transferred to the photo paper using a set of color filters and a swiveling mirror in the projection beam path of the printer.
The index print is produced and the requisite digital data is obtained in the exposure station of the photographic printer in both of these methods. A disadvantage of these methods is that they require significant extra expenditure for devices (high-resolution video camera, deflecting mirror, and so forth) in the exposure station of the printer, which is relatively expensive. Correct exposure control for producing the prints is also more difficult, because an unknown portion of the copying light intensity is deflected away from the exposure beam path.
Currently, photographic printers for producing photographic prints normally do not use standardized, uniform amounts of copying light. Rather, exposure control processes are employed, in which the most optimal possible amounts of copying light and in particular the exposure times for the three fundamental colors of blue, green and red are determined for the individual frames. To that end, in a scanning station preceding the exposure station of the printer, the individual frames of the negative films are analyzed by being photoelectrically scanned regionally using measurement light. The measurement light transmitted or remitted from each scanning region is delivered to a detector array, broken down spectrally, and converted into wavelength-and intensity-dependent electrical measurement signals. The electrical measurement signals are then digitized and utilized for ascertaining the amounts of copying light required.
U.S. Pat. Nos. 5,184,227 and 5,400,152 suggest that the scanning data, as determined by analyzing the originals in the scanning station of a printer using a locally high-resolution color scanner, be used to generate digital representations of the picture contents of the individual frames, and that the index prints be produced using these digital representations. To that end, the originals are scanned in the scanning station by the locally high-resolution color scanner, which for each scanning region measures the color densities in the three fundamental colors of red, green and blue. These scanning data per original are then used in their entirety to generate the digital representation of the picture content of this original. To ensure that the index prints will be of adequate quality and will give a good optical impression of the picture content, a high number of scanning regions is used. In U.S. Pat. No. 5,184,227, for instance, it is stated that each original is scanned with a resolution of 480 (vertical).times.252 (horizontal) scanning regions; that is, the original is assessed with respect to its color density in the colors of blue, green and red, in 120,960 scanning regions, arranged in the form of a 480.times.252 matrix. Although such high resolution is certainly advantageous with a view to high- quality index prints, it is a hindrance when using scanning data in determining the correct exposure times. With this amount of data, currently conventional methods used in exposure time calculation, including color and data corrections, cannot be implemented with reasonable effort and expense. For this reason, according to U.S. Pat. No. 5,184,227, when calculating the exposure time, the scanning data of a plurality of scanning regions are combined and reduced to a 24 (vertical).times.36 (horizontal) matrix, which is then used to calculate the exposure. It is known that a resolution on this order of magnitude is entirely sufficient for taking all the color information of a photographic original into account in calculating the exposure.
The method described in U.S. Pat. No. 5,184,227, of assessing the color of the original with very high local resolution and then reducing this data set for calculating the exposure, nevertheless also has disadvantages. Because of the high local resolution, the individual scanning regions are very small, and hence the measurement light intensities acting upon each of them are very slight. As a rule, this results in reduced measurement accuracy for the color density, since the signal to noise ratio is markedly poorer than when larger-area scanning regions are used. Still, for the most correct possible exposure calculation it is desirable that the color information be determined in a scanning region with the highest possible accuracy. Typically, in view of the correct exposure calculation, it is more advantageous to analyze the respective original with locally lower resolution which facilitates scanning larger areas resulting in a very high measurement accuracy with respect to the color information, as opposed to using a high local resolution in the scanning and to accept a reduced measurement accuracy with respect to the color information.
For this reason, in many modern photographic printers, when the photographic originals are scanned for their color composition, a low to medium local resolution is used. Typically, 39.times.26 scanning regions per original are used. The goal is to determine the most accurate color information of these scanning regions. To further increase the accuracy of the color information, it is known that instead of determining the three color densities in the fundamental colors of blue, green and red for each of the scanning regions, a spectral analysis is performed of the measurement light transmitted or remitted from the scanning region. In this method, the measurement light is examined with regard to its intensity, for instance, in 35 different wavelength ranges of the visible spectrum. Thus, instead of only three scanned values per scanning region, 35 scanned values are determined. Such a high spectral resolution per scanning region, in combination with a high local resolution of the color scanner as described above, would lead to data of relatively low accuracy with regard to the color information, and would also produce an amount of data that would be difficult to process at reasonable effort and expense.
On the other hand, local resolution of 39.times.26 scanning regions per original is normally too low to allow the data to be used directly as a digital representation of the picture content for producing index prints of adequately high quality. Typically, digital representations should have a resolution of at least 190.times.130 digital pixels, if the individual pictures on the index print are to have a high quality.